1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device and a pixel repairing method, which repair hot spot errors or dark spot errors of pixels formed at an outermost line (formed on a last horizontal line) among a plurality of pixel areas emitting light by using a dummy pixel.
2. Discussion of the Related Art
Organic light emitting display devices according to related art emit light from organic light emitting diodes (OLEDs) to display an image. The organic light emitting display devices include, depending on a driving type, passive matrix organic light emitting display devices and active matrix organic light emitting display devices.
A passive matrix organic light emitting display device includes a plurality of pixels being arranged in a matrix and not including thin film transistors (TFTs). In the passive matrix organic light emitting display devices, power consumption increases, and resolution is limited.
An active matrix organic light emitting display device has a plurality of TFTs respectively formed in a plurality of pixels which are arranged in a matrix type. Each of the plurality of pixels is driven according to a switching operation of a TFT and a voltage charged into a storage capacitor Cst.
The active matrix organic light emitting display devices have low power consumption and high resolution compared to the passive matrix organic light emitting display devices. An active matrix organic light emitting display device is suitable for a display device requiring a high resolution and a large area. For convenience, the present specification also refers to an active matrix organic light emitting display device is as an organic light emitting display device.
FIG. 1 is a circuit diagram for describing a pixel structure of a general organic light emitting display device. An equivalent circuit of one of a plurality of pixels which uses an external compensation method is formed in a display panel.
Each pixel of the display panel includes an OLED, which emits light with a data current Ioled applied thereto, and a pixel circuit PC which drives the OLED. Also, a plurality of lines for supplying a driving voltage and signals to the OLED and the pixel circuit PC are formed in the display panel.
Here, the pixel circuit PC includes a first switch TFT ST1, a second switching TFT ST2, a driving TFT DT, and a capacitor Cst. The plurality of lines includes a data line DL, a gate line GL, a driving voltage line PL, a sense signal line SL, and a reference voltage line RL.
The first switching TFT ST1 is turned on according to a scan signal (a gate driving signal) supplied to the gate line GL. The first switching TFT ST1 is turned on, and a data voltage Vdata supplied to the data line DL is supplied to the driving TFT DT.
The driving TFT DT is turned on with the data voltage Vdata supplied from the first switching TFT ST1. The data current Ioled flowing to the organic light emitting diode OLED is controlled with a switching time of the driving TFT DT.
When the scan signal is applied through the gate line GL, the first switching TFT ST1 is turned on. At this time, a signal from the first switching TFT ST1 is input to a gate electrode of the driving TFT DT, which is turned on. When the driving TFT DT is turned on, a driving current applied through the driving voltage line PL is input to the organic light emitting diode OLED, which emits light.
For external compensation, the sense signal line SL is formed in the same direction as that of the gate line GL. The second switching TFT ST2, which is turned on according to a sense signal applied through the sense signal line SL, is formed. The data current Ioled, which is supplied to the organic light emitting diode OLED according to the second switching TFT ST2 being turned on, is sensed by using an analog-to-digital converter (ADC) of a data driving integrated circuit (IC). A data voltage supplied to each pixel is compensated for according to a sense value of each pixel sensed by the ADC, thereby compensating for the changes in a threshold voltage “Vth” and mobility characteristic of the driving TFT DT.
Next, FIG. 2 is a plan view of a portion of a display area of a general organic light emitting display device, and is a view illustrating one unit pixel disposed on a last horizontal line among all the pixels. An area in which a pixel circuit is formed in each pixel area is defined as a pixel circuit area CA. The pixel circuit includes a driving TFT 20, a scan TFT 30, and a sense TFT 40. An area, in which an OLED is formed, is defined as an emission area EA.
A driving voltage line (VDD line) and a data line are formed in a vertical direction, and a gate line and a sense signal line (sense line) are formed in a horizontal direction. The emission area EA is defined by an intersection of a data line and a gate line. A plurality of pixels are formed in the emission area. A red pixel, a green pixel, a blue pixel, and a white pixel constitute one unit pixel 10. A pixel circuit area CA is defined between the gate line and the sense signal line.
A source electrode of the driving TFT 20 is connected to the driving voltage line, and a drain electrode is connected to an anode electrode of the OLED. A gate electrode of the driving TFT 20 is connected to a drain electrode of the scan TFT 30. A gate electrode of the scan TFT 30 is connected to the gate line, and a source electrode is connected to the data line. A gate electrode of the sense TFT 40 is connected to the sense signal line, a drain electrode is connected to the drain electrode of the driving TFT 20, and a source electrode is connected to a reference voltage line (Ref line).
Next, FIG. 3 is a diagram illustrating that a pixel in which a hot spot error occurs is repaired and blackened. When the driving TFT 20, the scan TFT 30, or the sense TFT 40 formed in one pixel area is not driven as normal, a dark spot error occurs because a current is not applied to an OLED. Also, when the source electrode of the driving TFT 20 is short-circuited with the drain electrode (i.e., a short circuit occurs between lines and metal layers), the driving TFT 20 in each pixel is not driven as normal, and a voltage applied to the source electrode may be directly applied to the drain electrode. In this case, the driving TFT 20 is maintained in a turn-on state without being turned off, and thus, a hot spot error occurs in which the OLED continuously emits light. When a dark spot error or a hot spot error occurs in a specific pixel, it is impossible to repair a blackened pixel area, and thus, a blackened state is maintained as-is.
A whitened pixel area is cut, through laser cutting, at a point A in which the driving TFT 20 of the pixel circuit driving a whitened pixel is connected to an anode electrode of the OLED. That is, a connection between the driving TFT 20 and the anode electrode of the OLED is cut by performing laser cutting in an open area between the storage capacitor and the anode electrode of the OLED.
Moreover, a point B in which the drain electrode of the sense TFT 40 is connected to the driving TFT 20 is cut through laser cutting. Also, the anode electrode is electrically connected via a welded OLED to a cathode electrode. The welded OLED is blackened due to the welded OLED being formed in the emission area EA of a pixel in which a hot spot error occurs.
Because a dark spot error is low in visibility, a user cannot recognize a dark spot error. On the other hand, since a hot spot error is high in visibility, the user can immediately recognize a hot spot error, and thus, a whitened pixel area is blackened.
When a dark spot occurs in only one hot spot in an entire area of the display panel, an error prevents production of the display device. On the other hand, when a dark spot occurs in ten to twenty pixels in the entire area of the display panel, a pixel area in which a hot spot error occurs can be repaired by blackening the pixel area.
As described above, a hot spot is repaired by blackening the pixel area but the hot spot is not fully repaired. For this reason, there is a limitation in increasing a yield rate of products. Since millions to tens of millions of pixel areas are formed in an organic light emitting display device, a display panel in which all pixel areas have no error is difficult to manufacture. Also, in a display panel in which all pixel areas have no error, a yield rate is reduced, causing an increase in the manufacturing cost.
In particular, when dark spots occur in pixel areas which are arranged on first to N-1st horizontal lines among N numbers of horizontal lines formed in the display panel, pixel areas formed at a lower portion of the display panel are repaired, and the dark spots are repaired by receiving signals from the pixel areas formed at the lower portion.
However, when dark spots occur in pixel areas (i.e., pixel areas formed on a last horizontal line) formed at an outermost portion among pixel areas (i.e., pixel areas emitting light) formed on an Nth horizontal line in the display panel, there are no pixels in lower portions of the display panel that can provide signals to pixels in the outermost portions of the display panel.